(Bloomberg) -- Shares of Ritchie Bros. Auctioneers Inc. fell the most on record after the Canadian company agreed to buy US auto retailer IAA Inc. in a cash-and-stock deal worth about $6.2 billion. 

Ritchie was down 18.2% to $50.91 as of 3:17 p.m. in New York, its biggest-ever decline and taking the shares to the lowest point since May. 

“Investors view RBA as counter-cyclical,” National Bank of Canada analyst Maxim Sytchev said a note, referring to Ritchie’s stock ticker. Its core business is selling used industrial and construction equipment, a business that can perform well in tough economic times. 

“We are more bullish on the construction market given North American infra plans but autos are now facing some tough backdrop,” Sytchev wrote.

IAA shareholders will receive $10 in cash and 0.5804 of a Ritchie share for each IAA share they own, the companies said Monday. The deal includes Ritchie assuming $1 billion of IAA’s debt.

“The transaction will diversify Ritchie Bros.’ customer base by providing the company with a significant presence in the vehicle remarketing vertical that has strong industry fundamentals with proven secular growth,” Ritchie Bros said in the statement.

The purchase price of $46.88 a share represents a premium of about 19% to IAA’s closing price on Friday, according to the statement. But with the decline in Ritchie’s share price, IAA was down 2% on Monday afternoon.  

“The financials actually do make sense” for Ritchie, Sytchev said on BNN Bloomberg Television. But, he added, “people own shares for specific reasons and when the investment thesis around a stock changes dramatically, that’s the kind of share price reaction that you do witness.” 

(Updates with share price, analyst comment)

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